Develop Reference

SqlDataReader not reading data from database

I'm trying to set up a login for my project, so I'm using SqlCommand to make the command and then I use SqlDataReader to read the data from the database, but whenever I try to read it the reader appears to be empty.
When I was debugging the app I noticed that the connection wasn't showing the complete version with the password, and I searched around and found out that it doesn't show it for security reasons, so I tried to use Persist Security Info = true but it didn't work.
Here is my connection:
SqlConnection connection = new SqlConnection("Server=.\\SQLEXPRESS;Database=BD_GA;Uid=sa;Pwd=SQL_;Persist Security Info=True");
My code for the login:
connection.Open();
SqlCommand commandLogin = new SqlCommand("select * from Proprietário", connection);
SqlDataReader reader = commandLogin.ExecuteReader();
while (reader.Read())
{
if (reader.GetValue(5).ToString() == txtUser.Text && reader.GetValue(6).ToString() == txtPass.Text)
{
User = txtUser.Text;
tipo = reader.GetBoolean(7);
tssl_Login.Text = "Login feito com sucessso!";
break;
}
}
It should say "Login feito com sucesso" if it works but it doesn't show anything.

Please try these details below
Connection
SqlConnection connection = new SqlConnection("Data Source = .\\SQLEXPRESS;
Database = BD_GA;User ID = sa;Password = SQL_;Integrated Security = true;
Encrypt = False; TrustServerCertificate = True; ApplicationIntent = ReadWrite; MultiSubnetFailover = False");
If there is something wrong with connection it will show the error message.
try
{
connection.Open();
SqlCommand commandLogin = new SqlCommand("select * from Proprietário", connection);
SqlDataReader reader = commandLogin.ExecuteReader();
while (reader.Read())
{
if (reader.GetValue(5).ToString() == txtUser.Text && reader.GetValue(6).ToString() == txtPass.Text)
{
User = txtUser.Text;
tipo = reader.GetBoolean(7);
tssl_Login.Text = "Login feito com sucessso!";
break;
}
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
connection.Close();
}

I didn't get error when try to connect SQL Server

I have a Virtual Machine in Windows Azure with SQL Server 2016. This VM has a firewall with Azure, where I allow the IP to connect to the server. And also my project is an ASP.NET Web API 2 with ADO.NET for Data Access Layer.
The thing is all set; everything is working fine (Good!). But If I try to connect from another place with an IP that is not added to the firewall rules, I don't get any error, only still to try to execute the command. Normally if I use the SQL Managment I get an error.
This is my parameter in my connection string
Server=vm.XXXXXX.azure.com;Database={database};User ID={userid};Password={password};Encrypt=True;TrustServerCertificate=True;Connection Timeout=300;ConnectRetryCount=4;ConnectRetryInterval=1
So, this is extract code that I executed:
using (SqlConnection dbConnection = new SqlConnection(myCString))
{
using (SqlCommand dbCommand = new SqlCommand())
{
string queryString;
queryString = "SELECT * FROM table WHERE (ID = #ID) ";
dbCommand.Parameters.Add(Utilities.GetSQLParameter("ID", 1234, SqlDbType.VarChar));
dbCommand.CommandText = queryString;
dbCommand.Connection = dbConnection;
dbConnection.Open();
using (SqlDataReader dr = dbCommand.ExecuteReader())
{
if (dr.Read())
{
Value = dr[Field].ToString();
}
else
{
Value = "";
}
}
}
}
In summary, I want to get the error if I cannot find the VM because the firewall is blocking the access.

The connection failure occurs at dbConnection.Open.
Wrap your code in atry/catch block and treat the error if it occurs.
A list of available catchable exceptions can be found at https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.open(v=vs.110).aspx
try
{
dbConnection.Open();
using (SqlDataReader dr = dbCommand.ExecuteReader())
{
if (dr.Read())
{
Value = dr[Field].ToString();
}
else
{
Value = "";
}
}
}
catch(Exception ex)
{
//Do some treatment
}
finally
{
//If connection has been opened, close it.
if(dbConnection.ConnectionState == ConnectionState.Open)
{
dbConnection.Close();
}
}

I will recommend you use USING clear all your "managed resources"
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-statement
using (SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["ConnStringName"].ToString()))
using (SqlCommand mySqlCommand = new SqlCommand())
{
try
{
conn.Open();
mySqlCommand.Connection = conn;
mySqlCommand.CommandType = CommandType.StoredProcedure;
mySqlCommand.CommandText = "getCities";
mySqlCommand.CommandTimeout = Convert.ToInt32(System.Configuration.ConfigurationManager.AppSettings["ConnectionTimeout"].ToString());
mySqlCommand.Parameters.Add("#param", SqlDbType.VarChar).Value = param;
da.SelectCommand = mySqlCommand;
da.Fill(ds, "cities");
}
catch (Exception ex)
{
// LOG HERE the errors
}
} // end using

Unable to Get value from MySQL and print to TextBox

So this method is supposed to get the ipaddress of the logged in user from a MySQL Database and print it to a textbox. However, I cant seem to get it right as the program just closes after I execute this method.
public void readIPAddress()
{
string username = GlobalData._sharedUserName;
String connString = System.Configuration.ConfigurationManager.ConnectionStrings["WebAppConnString"].ToString();
conn = new MySql.Data.MySqlClient.MySqlConnection(connString);
conn.Open();
queryStr = "";
queryStr = "SELECT ipaddress FROM webappdemo.userregistration WHERE username=?username";
cmd = new MySql.Data.MySqlClient.MySqlCommand(queryStr, conn);
cmd.Parameters.AddWithValue("?username", username);
cmd.ExecuteReader();
while (cmd.ExecuteReader().Read())
{
textBoxIPAddress.Text = reader["ipaddress"].ToString();
}
conn.Close();
}
If anyone could point out where I went wrong, I greatly appreciate your help!
Edit: After using try and catch I get this:
MySql.Data.MySqlClient.MySqlException (0x80004005): There is already an open DataReader associated with this Connection which must be closed first.
at MySql.Data.MySqlClient.ExceptionInterceptor.Throw(Exception exception)
at MySql.Data.MySqlClient.MySqlConnection.Throw(Exception ex)
at MySql.Data.MySqlClient.MySqlCommand.CheckState()
at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior)
at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader()
at ConnectToDataBase.Form2.readIPAddress() in C:\Users\ee\Dropbox\ConnectToDataBase\ConnectToDataBase\Form2.cs:line 95

Quick Fix:
You are executing the command two times, using ExecuteReader that's why you are getting such exception. If you execute the code like this means your code will works fine:
string queryStr = "SELECT ipaddress FROM webappdemo.userregistration WHERE username=#username";
using (MySqlConnection conn = new MySqlConnection(connString))
{
conn.Open();
using (MySqlCommand cmd = new MySqlCommand(queryStr, conn))
{
cmd.Parameters.AddWithValue("#username", username);
var reader = cmd.ExecuteReader();
while (reader.Read())
{
textBoxIPAddress.Text = reader["ipaddress"].ToString();
}
}
}
Smart Fix:
Here you are fetching a single value from the database in such situations you need not to use reader at all. you can simply access those value by using ExecuteScalar() method, which will give you the required object. if so You can use the following code:
using(MySqlConnection conn = new MySqlConnection(connString))
{
using(MySqlCommand cmd= new MySqlCommand(query, conn))
{
cmd.Parameters.Add("#username", username);
conn.Open();
object ipAddress= cmd.ExecuteScalar();
if (ipAddress!= null)
textBoxIPAddress.Text = ipAddress.ToString();
else
textBoxIPAddress.Text = "No data found";
}
}
Hope that you wont forget to add MySql.Data.MySqlClient; to the using section

you are executing reader two times by calling ExecuteReader(), why you need Reader here, if you only need one value from database. use ExecuteScalar that will return first value of the first record from the result. Sample code:
try
{
string query = "SELECT ipaddress FROM webappdemo.userregistration WHERE username = #username";
string connString =ConfigurationManager.ConnectionStrings["WebAppConnString"].ToString();
using(MySqlConnection connection = new MySqlConnection(connString))
{
using(MySqlCommand command = new MySqlCommand(query, connection))
{
command.Parameters.Add("#username", username);
connection.Open();
object ip= command.ExecuteScalar();
if (ip != null) {
textBoxIPAddress.Text = ip.ToString();
}
}
}
}
catch(MySqlException ex)
{
// do something with the exception
}

Problem:
cmd.ExecuteReader(); //Executing reader and not assigning to anything
while (cmd.ExecuteReader().Read()) //Executing reader again and not assigning to anything again
{
//There is nothing assigned to reader.
textBoxIPAddress.Text = reader["ipaddress"].ToString();
}
Quick Solution:
//assuming reader is defined
reader = cmd.ExecuteReader();
while (reader.Read()) //read from the reader
{
textBoxIPAddress.Text = reader["ipaddress"].ToString();
}
Alternative Solutions using MySql.Data.MySqlClient.MySqlHelper:
try {
object ip = MySqlHelper.ExecuteScalar(connString, query, new MySqlParameter[] {
new MySqlParameter("?username", username)
}));
if (ip != null) {
textBoxIPAddress.Text = ip.ToString();
}
} catch (Exception ex) {
// do something with the exceptio
}
If you insist on using reader:
//assuming reader is defined
reader = MySqlHelper.ExecuteReader(connString, query, new MySqlParameter[] {
new MySqlParameter("?username", username)
}));
while (reader.Read()) //read from the reader
{
textBoxIPAddress.Text = reader["ipaddress"].ToString();
}
Note: the above code is just typed in here and may contain syntax errors. take this a a guideline.

C# & .NET request: On mySQL connection my app says: “The given key was not present in the dictionary”

I browsed many answers with "The given key was not present in the dictionary", but the problems were always bad usage of parameters. I'm not using any parameters and still get this error. Any help?
string connection = "Server=db4free.net;Database=rmkhu;Uid=rmkrmk;Pwd=***;";
MySqlConnection con = new MySqlConnection(connection);
MySqlCommand command = con.CreateCommand();
command.CommandText = "Select * FROM drpciv_hu";
try
{
con.Open();
MySqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
label7.Text = reader["kerdes"].ToString();
}
}
catch (Exception ex)
{
label7.Text = ex.Message;
}
When I run this code I get catch (Exception ex).
ex.Message = The given key was not present in the dictionary

Error: The type 'System.Data.OleDb.OleDbDataReader' has no constructors defined

I am trying to change password option with ms access database....
please help me folks....
here the code:
default.aspx.cs
protected void Button1_Click(object sender, EventArgs e)
{
try
{
OleDbConnection myCon = new OleDbConnection(ConfigurationManager.ConnectionStrings["vhgroupconnection"].ConnectionString);
myCon.Open();
string userid = txtuserid.Text;
string oldpass = txtoldpass.Text;
string newPass = txtnewpass.Text;
string conPass = txtconfirmpass.Text;
string q = "select user_id,passwd from register where user_id = #userid and passwd = #oldpass";
OleDbCommand cmd = new OleDbCommand(q, myCon);
OleDbDataReader reader = new OleDbDataReader();
cmd.Parameters.AddWithValue("#userid", txtuserid.Text);
cmd.Parameters.AddWithValue("#oldpass", txtoldpass.Text);
reader = cmd.ExecuteReader();
reader.Read();
if (reader["user_id"].ToString() != String.Empty && reader["passwd"].ToString() != String.Empty)
{
if (newPass.Trim() != conPass.Trim())
{
lblmsg.Text = "New Password and old password does not match";
}
else
{
q = "UPDATE register SET passwd = #newPass WHERE user_id =#userid";
cmd = new OleDbCommand(q, myCon);
cmd.Parameters.AddWithValue("#newPasss", txtnewpass.Text);
cmd.Parameters.AddWithValue("#userod", txtuserid.Text);
cmd.Parameters.AddWithValue("#passwd", txtoldpass.Text);
int count = cmd.ExecuteNonQuery();
if (count > 0)
{
lblmsg.Text = "Password changed successfully";
}
else
{
lblmsg.Text = "password not changed";
}
}
}
}
catch (Exception ex)
{
throw ex;
}
}
also check pls.....
Compilation Error Description: An error occurred during the
compilation of a resource required to service this request. Please
review the following specific error details and modify your source
code appropriately.
Compiler Error Message: CS0143: The type
'System.Data.OleDb.OleDbDataReader' has no constructors defined
Source Error:
Line 36: OleDbCommand cmd = new OleDbCommand(q, myCon);
Line 37:
Line 38: OleDbDataReader reader = new OleDbDataReader();
Line 39:
Line 40:

As error message says; OleDbDataReader has no constructor.
From documentation of OleDbDataReader;
To create an OleDbDataReader, you must call the ExecuteReader method
of the OleDbCommand object, instead of directly using a constructor.
You can use ExecuteReader method that returns OleDbDataReader
OleDbDataReader dr = cmd.ExecuteReader();
And you need add your parameter values before you call ExecuteReader method.
Also use using statement to dispose your OleDbConnection, OleDbCommand and OleDbDataReader like;
using(OleDbConnection myCon = new OleDbConnection(conString))
using(OleDbCommand cmd = myCon.CreateCommand())
{
//Define your sql query and add your parameter values.
using(OleDbDataReader dr = cmd.ExecuteReader())
{
//
}
}
And as Steve mentioned, OleDbDataReader.Read method returns boolean value (true of false) and it reads your OleDbDataReader results row by row. You might need to consider to use the result of this method like in a while statement. For example;
while(reader.Read())
{
//Reads your results until the last row..
}
As a final words, I strongly suspect you store your passwords as plain text. Don't do that! Use SHA-512 hash.

As MSDN clearly states, To create an OleDbDataReader, you must call the ExecuteReader method of the OleDbCommand object, instead of directly using a constructor.
You cannot instantiate it using new, which is what you are doing and which is why you get the error. Remove the offending line and change it to this to get rid of the error:
OleDbDataReader reader = cmd.ExecuteReader();
Also, remember to use using blocks to ensure resources get properly disposed.
using(OleDbConnection myCon = new OleDbConnection(ConfigurationManager.ConnectionStrings["vhgroupconnection"].ConnectionString))
{
OleDbCommand cmd = new OleDbCommand(q, myCon);
//Add parameters etc
OleDbDataReader reader = cmd.ExecuteReader();
//Rest of the processing
}

Problem: You try to make new instance of OleDbDataReader by calling new OleDbDataReader() instead you should create a reader using OleDbCommand.ExecuteReader().
In the following code notice use of using statement (this should ensure connection closing or reader closing for the case of OleDbDataReader).
protected void Button1_Click(object sender, EventArgs e)
{
try
{
string sConnString = ConfigurationManager.ConnectionStrings["vhgroupconnection"].ConnectionString;
using(OleDbConnection myCon = new OleDbConnection(sConnString))
{
myCon.Open();
string userid = txtuserid.Text;
string oldpass = txtoldpass.Text;
string newPass = txtnewpass.Text;
string conPass = txtconfirmpass.Text;
string q = "select user_id,passwd from register where user_id = #userid and passwd = #oldpass";
OleDbCommand cmd = new OleDbCommand(q, myCon);
cmd.Parameters.AddWithValue("#userid", txtuserid.Text);
cmd.Parameters.AddWithValue("#oldpass", txtoldpass.Text);
string sUserId = string.Empty;
string sPass = string.Empty;
using(OleDbDataReader reader = cmd.ExecuteReader())
{
if(reader.Read()) //assumption: one record returned
{
sUserId = reader["user_id"].ToString();
sPass = reader["passwd"].ToString();
}
}
if (sUserId != string.Empty && sPass != string.Empty)
{
if (newPass.Trim() != conPass.Trim())
lblmsg.Text = "New Password and old password does not match";
else
{
q = "UPDATE register SET passwd = #newPass WHERE user_id =#userid";
cmd = new OleDbCommand(q, myCon);
cmd.Parameters.AddWithValue("#newPass", txtnewpass.Text);
cmd.Parameters.AddWithValue("#userid", txtuserid.Text);
int count = cmd.ExecuteNonQuery();
if (count > 0)
lblmsg.Text = "Password changed successfully";
else
lblmsg.Text = "password not changed";
}
}
}
}
catch (Exception ex)
{
throw ex;
}
}